1. Field of the Invention
The present invention relates to a recording medium discriminating method for discriminating the type of a recording medium, a recording apparatus having a function of discriminating the type of a recording medium, a program for executing the discrimination as to the type of a recording medium, and a storage medium storing the program. More particularly, the present invention relates to a technique for discriminating the type of a recording medium from image information regarding a surface of the recording medium.
2. Description of the Related Art
Hitherto, various types of output devices, such as electrophotographic, wired-dot, and ink-jet devices, have been practiced as output devices of printing systems in which a color image is formed by attaching colored toners or inks to a recording surface of a recording medium and then ejecting the recording medium having the color image recorded thereon.
Of those output devices, the ink-jet device has garnered a lot of attention because such a device directly ejects inks from a recording head to the recording medium. This device, thus, requires fewer number of steps to form an image on the recording medium than other devices, and has additional advantages such as a low running cost, being suitable for color recording, and it produces less noise during the recording operation. For these reasons, the ink-jet device has received attention in a variety of markets ranging from business to domestic fields. Recently, many recording apparatuses (printers), facsimile machines, and copying machines have been practiced using output devices of the ink-jet type.
It is generally known that various types of recording media are employed in an ink-jet recording apparatus. The types of recording media include plain paper, typically used regardless of the recording scheme, ink-jet coated paper (including a postcard dedicated for ink-jet printing, such as a New Year's card having the postcard size) in which a coating agent, e.g., silica, is applied to the recording surface of the recording medium for suppressing ink blurring and improving color development. Other recording media include: glossy paper and glossy film, which have a glossy appearance on the recording surface of the recording medium similar to photographic paper for glossy print, and which are used for forming photographs and images; an OHP film for a transparent document; transfer paper for transferring an image to a cloth, e.g., using an iron to transfer the image to a T-shirt, after recording the image on the recording medium; and a back print film in which a back surface of the recording medium serves as a recording surface. Thus, there are various types of recording media including others that are familiar to users.
In the ink-jet recording apparatus, because permeability and fixity of ink differ depending on the coating agent applied to the surface of the recording medium, recording conditions for obtaining a good recorded image differ depending on the type of the recording medium. As a result, before the recording process begins, the user must select or enter the type of recording medium on which the image is to be recorded into the system and must set a recording mode suitable for the recording medium. In so doing, if the user erroneously sets the type of the recording medium and the recording mode by mistake, a recording image having the quality demanded by the user cannot be obtained in some cases. To avoid the troublesome operation required by the user and the possibility of a false setting, a device for automatically discriminating the type of the recording medium and then selecting and setting an optimum recording mode has been created. This automatic setting of a suitable recording mode for the type of the recording medium is needed in not only the ink-jet recording apparatus, but also in other types of recording apparatuses.
FIG. 35 shows one example of a method for discriminating the type of the recording medium. With this method, a light is illuminated from a light source to a recording medium, and a reflected light from a surface of the recording medium is detected by an optical sensor using a photoelectric transducer to measure the intensity of the reflected light. Referring to FIG. 35, a light source 3501 illuminates a light at an angle θ of incidence (arbitrary value) to a recording medium 3504 of which type is to be determined. A light receiving device 3502 for measuring the intensity of a specular reflection light receives a light that has been reflected at an angle θ of reflection equal to the angle θ of incidence at which the light was illuminated from the light source 3501. Because the intensity of the specular reflection light changes depending on a gloss of the recording medium surface, the gloss of the recording medium can be confirmed by measuring the intensity of the specular reflection light. Further, a light receiving device 3503 receives a light having diffusely reflected at an angle different from the angle θ of incidence, at which the light was illuminated from the light source 3501, (e.g., a light having reflected at a right angle relative to the recording medium in FIG. 35), for measuring the intensity of a diffuse reflection light. Because the intensity of the diffuse reflection light changes depending on the whiteness of the recording medium surface, the whiteness of the recording medium can be confirmed by measuring the intensity of the diffuse reflection light. The light source 3501 and the light receiving device 3502 receiving the specular reflection light are set in a layout such that the specular reflection light having reflected from the recording surface of the recording medium 3504 subjected to illumination from the light source 3501 can be received by the light receiving device 3502. Likewise, the light source 3501 and the light receiving device 3503 receiving the diffuse reflection light are set in a layout such that the diffuse reflection light having reflected from the recording surface of the recording medium 3504 subjected to illumination from the light source 3501 can be received by the light receiving device 3503. By comparing values of the intensity of two reflected lights thus obtained with corresponding values of the intensity of two reflected lights measured in advance for each type of the recording medium to be used, the type of the recording medium is discriminated.
Japanese Patent Laid-open No. 11-271037 discloses an image forming method and an image forming apparatus for forming a high-quality image without regard to the type of the recording medium used and surface roughness thereof. In the disclosed method and apparatus, surface roughness is detected by measuring, as three-dimensional image information, an intensity distribution of a reflected light from a recording medium obtained when a light from a light source is illuminated to the recording medium, and then converting the detected information into a fractal dimension, i.e., one-dimensional information. A toner amount is then controlled to be matched with the surface roughness of the recording medium.
Also, the assignee of the present application has previously proposed a discriminating device and a discriminating method in which, with a system employing a plurality of light receiving devices, the type of the recording medium is discriminated based on a gloss of the recording medium surface and fiber orientation of the recording medium surface. With this method, the fiber orientation of the recording medium surface is detected from a variation in intensity of diffuse reflection light sensed by the plurality of light receiving devices.
The related art described above, however, has problems as follows.
FIG. 36 shows the relationships of various types of recording media versus the intensity of the specular reflection light and the intensity of the diffuse reflection light. In FIG. 36, numeral 3601 represents a distribution region of plain paper in terms of the intensity of the specular reflection light and the intensity of the diffuse reflection light. Likewise, numerals 3602, 3603, 3604, 3605 and 3606 represent distribution regions of ink-jet coated paper, glossy paper, photographic glossy paper, a glossy film, and an OHP film, respectively. As seen from FIG. 36, it is difficult to accurately discriminate plain paper and ink-jet coated paper from the relationships between the recording media and two reflected-light components, i.e., the specular reflection light and the diffuse reflection light.
The intensity of the specular reflection light representing the gloss of the recording medium is given a value corresponding to the surface roughness so long as the recording medium is formed of the same material (although the intensity of the specular reflection light is indirectly affected by not only a surface layer, but also an intermediate layer). Accordingly, the intensity of the specular reflection light can be used as a parameter for discriminating the type of the recording medium. However, because various types of recording media are formed of a variety of different materials, there is a possibility that different types of recording media in fact provide values of the intensity of the specular reflection light comparable to each other. Such a case is confirmed, by way of example, with plain paper and ink-jet coated paper. Ink-jet coated paper has a higher smoothness (which is increased as the recording medium has a flatter and smoother surface) than plain paper, and therefore it provides a greater intensity of the specular reflection light if the recording medium is formed of the same material. However, light diffusion by the ink-jet coated paper is increased with the presence of a pigment, e.g., silica, applied to its surface. As a result, the value of the intensity of the specular reflection light from the ink-jet coated paper is comparable to or slightly smaller than that of the plain paper.
Further, many types of plain paper and ink-jet coated paper provide close values of the intensity of the diffuse reflection light that represents whiteness of the recording medium. The reason is that users prefer recording media having a high degree of whiteness, which make black characters appear more tightly and provide a better color tint of a photographic image. In the past, placing a coat of calcium carbonate on the recording medium surface has been avoided for the problem that calcium carbonate scrapes a fusing roller used in an image forming apparatus employing the electrophotographic technique, such as a copying machine. Recently, however, calcium carbonate has been widely coated because of increased durability of the fusing roller. The coating of calcium carbonate is effective in increasing the whiteness of the recording medium, but it becomes difficult to discriminate plain paper having high whiteness because of a coating of calcium carbonate from ink-jet coated paper.
Thus, in a conventional system employing reflection optical sensors for measuring the intensity of the specular reflection light and the intensity of the diffuse reflection light, it is difficult to discriminate plain paper and ink-jet coated paper from each other. This leads to a serious problem in an ink-jet recording apparatus in which recording conditions, such as the amount of ejected ink and the number of scans, i.e., passes, of a recording head for recording a one-line image differ depending on the type of the recording medium. In the above-mentioned two types of recording media, particularly, a significant difference exists in the recording conditions and hence a serious image quality problem results as well.
Also, in electrophotographic recording apparatuses other than the ink-jet recording apparatus, if users mistakenly place ink-jet coated paper instead of plain paper in a cassette storing the recording medium, there is a risk that the recording medium will wrap around the fusing roller and cause a paper jam. In other words, the necessity of accurately discriminating various types of recording media for ink-jet printing, which are widely put into the market, is a problem not restricted to the field of ink-jet recording apparatuses.
To solve the above-mentioned problem, the inventors have studied as a method of discriminating plain paper and ink-jet coated paper from each other with high accuracy, a method wherein the features of the surface roughness and the surface shape of a recording medium are obtained from image information regarding a surface of the recording medium by using an image sensor, as shown in FIG. 37, and then discriminating the type of the recording medium. Here, the surface roughness implies a feature regarding the magnitude of unevenness of the recording medium surface, and the surface shape implies a feature regarding the period of unevenness of the recording medium surface.
FIG. 37 is a schematic view showing a sensor system for discriminating the type of the recording medium by using the image sensor.
Referring to FIG. 37, a light source 3701 illuminates a light at an angle θ of incidence (arbitrary value) to a recording medium 3703 of which type is to be discriminated. Also, an image sensor 3702 creates image information regarding a surface of the recording medium from a component of diffuse reflection light having reflected at an angle different from the angle θ of incidence at which the light was illuminated from the light source 3701 (in FIG. 37, a light having reflected at a right angle relative to the recording medium). The light source 3701 and the image sensor 3702 are set in a layout such that the diffuse reflection light having reflected from the recording surface of the recording medium 3703 subjected to illumination from the light source 3701 can be received by the image sensor 3702.
By comparing parameters representing surface conditions of the recording medium obtained from the image information resulting from the above-described sensor system with corresponding parameters measured in advance and representing surface conditions of the recording medium of the type which is to be used, the type of the recording medium is discriminated. FIG. 38 shows the relationships of various types of recording media versus a brightness difference and an average value of brightness. Those relationships are obtained when employing, as two examples of the parameters representing surface conditions of the recording medium, the brightness difference, i.e., the difference between maximum and minimum values of brightness in image information comprising a plurality of pixels, and the average value of the brightness. Numeral 3801 represents a distribution region of plain paper. Likewise, numerals 3802, 3803, 3804, 3805 and 3806 represent distribution regions of ink-jet coated paper, glossy paper, photographic glossy paper, a glossy film, and an OHP film, respectively. As seen from FIG. 38, it is possible to discriminate plain paper and ink-jet coated paper based on the plotted relationship.
With the above-described system using the image sensor, plain paper and ink-jet coated paper, which have been usually employed for recording in the past, can be discriminated from each other. However, it is difficult to discriminate several types of recording media used in high quality image recording.
More specifically, while attention has been recently focused on photographic glossy paper, which is a recording medium capable of recording an image with a quality comparable to that of a photograph printed on photographic paper, and on a glossy film using white PET, etc. as a base, it is difficult to accurately discriminate those two types of recording media because both recording media have high gloss values. The reason is that, as a result of various improvements in recording an image with a quality comparable to that of a photograph printed on photographic paper, photographic glossy paper has a higher smoothness than conventional glossy paper, thus the glossy film and the photographic glossy paper have similar physical properties, such as surface roughness and surface shape.